1. Field
The present invention relates to a lithographic apparatus and a method for manufacturing a device.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In a measurement phase, during which the substrate surface is characterized, and an exposure phase, during which the desired pattern is imaged onto the substrate by the patterned radiation beam, the substrate is supported on a substrate table that is movable relative to the projection system. A drive mechanism is provided for driving the movement of the substrate table.
In order to minimize the distance traveled by the substrate table when switching between the measurement phase and the exposure phase, and when unloading and loading a substrate to/from the substrate table, it has been found convenient in prior art systems to use so-called planar motors to drive movement of the substrate table. These planar motors are implemented by attaching coils to the substrate table and permanent magnets to a body beneath the substrate table. The coils are driven in such a way as to cause the required accelerations and decelerations associated with the intended movement of the substrate table. The coils and permanent magnets car also be configured to cause levitation of the substrate table above the permanent magnets.
The planar motor configuration provides for movement that is relatively unconstrained spatially, and any connections between the substrate table and other parts of the lithography apparatus can stay constant during transfer of the substrate table from the measurement phase to the exposure phase; there is no need for the substrate table to be transfer -red from one drive mechanism to another drive mechanism, for example.
A problem with the use of such planar motors is that they are relatively inefficient, requiring a large amount of power to achieve the movement required. This increases cost and may limit the extent to which such systems can be used for processing larger substrates (which will require larger substrate tables and therefore larger forces) and/or increasing throughput (which will require larger accelerations and therefore larger forces).